16-11-2012, 01:06 PM
DC MOTOR
DC MOTOR1.docx (Size: 546.62 KB / Downloads: 29)
Principle:
When a current carrying conductor is placed in magnetic field it experiences a ‘mechanical force’.
In practical dc motor, field winding produces a required magnetic field while armature is a current carrying conductor and it experiences a force. As conductor are placed in slots which are on the individual force experienced by the conductor acts as twisting or turning force on the armature which is called a torque.
Significance of Back E.M.F:
After motoring action, there exists a generating action. There is an induced e.m.f in the rotating conductor according to Faraday’s law of electromagnetic induction. This induced e.m.f in the armature always acts in the opposite direction of the supply voltage. This is according to Lenz’s law which states that the direction of induced e.m.f is always so as to oppose the cause producing it. This induced e.m.f always opposes the supply voltage, it is called back e.m.f. It is denoted by Eb.
Voltage Equation of a D.C motor:
In d.c motor supply voltage V has to overcome back e.m.f Eb which is opposing v and also various drops as armature resistance drop IaRa, brush drop etc. Infant the electrical work done in overcoming the back e.m.f gets converted into the mechanical energy developed in the armature.